Although reporting on first lien mortgages with piggyback seconds has improved greatly, the rating agencies nonetheless have adopted additional protections for investors in residential MBS pools that contain simultaneous second-lien loans. The growing popularity of piggyback loan products – 80-10-10s, 80-20s and other combinations – has pushed their presence in residential MBS from single digits to 25-30 percent of many pools. And the rating agencies say the reason for this is the increased demand…